JP2833820B2 - Surface treatment method of titanium oxide - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for titanium oxide which is widely used as a white pigment in various paints, paper sizing agents, plastic fillers, and the like.

[Conventional technology]

Titanium oxide is usually subjected to various surface treatments for the purpose of improving weather resistance and dispersibility. Among them, treatment with aluminum oxide hydrate is one of the most common methods, and treatment by itself or in combination with another treating agent such as silica or zinc oxide is known. .

By the way, the treatment with aluminum oxide hydrate is usually performed by, for example, U.S. Pat.
No. 6,699 uses the following procedure.

A predetermined amount of titanium oxide is added to water to form a slurry.

Adjust the slurry temperature to a predetermined range.

A soluble aluminum compound is added and dissolved in the slurry.

While maintaining the pH within a predetermined range, an acid or alkali precipitant is added.

Aging is performed at a predetermined temperature and a predetermined pH for a predetermined time.

Also, in Japanese Patent Application Laid-Open No. 55-154317, the surface treatment step is referred to as a `` deposition step '', and the treatment procedure is `` 100 to 500 g / titanic acid or titanium dioxide, preferably 250 to 400 g /
Disperse in water to a concentration of (as TiO ₂ )
Aqueous slurry, sodium aluminate and, if necessary, a dispersing agent are added to disperse titanic acid or titanium dioxide well, and then neutralized with acid to deposit aluminum hydrated oxides. ing.

[Problems to be solved by the invention]

Each of the above treatment methods is characterized in that a soluble aluminum compound is dissolved in a slurry containing titanium oxide to cause a precipitation reaction, and simultaneously with the reaction, aluminum oxide hydrate is deposited on the titanium oxide surface.

However, when the soluble aluminum compound comes into contact with the acid or base precipitant, a sol of aluminum oxide hydrate is instantaneously formed at a pH of about 5 to 9.5. Therefore, in the conventional method, in which a surface treatment reaction is carried out by dropping an acid onto a titanium oxide slurry containing sodium aluminate, the formation of the sol and the surface treatment reaction proceed simultaneously. The result is to be performed under pH. This leads to non-uniformity of the surface treatment state and the presence of gelled aluminum oxide hydrate that does not deposit on the titanium oxide surface.

In order to prevent these problems, as shown in the first example of the "prior art", a method of simultaneously dropping an acid and a base to keep the pH during the surface treatment reaction uniform has been adopted. However, even in such a case, it is necessary to increase the time required for surface treatment in order to maintain pH uniformity, and the processing capacity of the apparatus is extremely limited because of the premise of batch processing. was there.

[Means for solving the problem]

The present inventors have conducted various studies to improve these problems.As a result, when performing surface treatment on titanium oxide with aluminum oxide hydrate, an aqueous dispersion slurry of titanium oxide and alumina sol were prepared in advance, We have found a method of surface treating titanium oxide, characterized by mixing these.

According to the present invention, the pH at the time of surface treatment can be kept almost constant by separately performing the production of a dispersion slurry of titanium oxide and the production of alumina sol to be subjected to the surface treatment,
The time required for surface treatment can be significantly reduced. Further, the surface treatment reaction itself can be continuously performed.

 Next, the processing method according to the present method will be described in more detail.

The titanium oxide to be subjected to the surface treatment may be either rutile or anatase. The particle size of titanium oxide is 0.
Any size is possible as long as it is in the range of 01 μ to 10 μ. If it is smaller than 0.01 μm, the difference in particle size from the fine particles constituting the alumina sol will be small, and the state of the surface coating will be poor. If the particle size is larger than 10μ, the treatment by this method is not impossible,
It is not suitable for practical use because the optical properties as a pigment, for example, the hiding power and the like are greatly reduced.

The alumina sol used in the present invention is produced as follows.

Dissolve the basic or acidic salt of aluminum in pure water and add acid or alkali to each to adjust the pH to 5-
It is usually generated by setting an appropriate value of 9.5.
In that case, the temperature is desirably set at 40 ° C to 90 ° C.
The order of addition and mixing may be reversed. That is, after adding an acid or alkali to water in advance, a basic salt or an acidic salt of aluminum may be added to each of them, or both may be added simultaneously or alternately.

It is desirable to use the sol immediately after the formation of the sol for the surface treatment reaction. This is because over time after sol formation, TiO ₂
This is because deposition on the surface is inferior and gelation occurs.

Other methods for producing an alumina sol include a method of hydrolyzing an organic compound such as a basic salt of aluminum or aluminum alkoxide, or a method of forming boehmite or pseudo-boehmite into a sol in an acidic region.

It is preferable that the ion exchange treatment is performed in a sol state to remove unnecessary ions and salts, thereby increasing the purity of the produced alumina sol.

The sol concentration of the alumina sol produced by any of the above methods is within a concentration range in which the sol does not gel.
It is determined depending on the final surface treatment amount for titanium oxide. The maximum sol concentration is about 5 mol / in terms of Al (OH) ₃ , though it varies somewhat depending on the sol production method.

The surface treatment amount of titanium oxide is 1 to 20 parts by weight in terms of alumina (Al ₂ O ₃ ) of aluminum oxide hydrate per 100 parts by weight of titanium oxide for general use. Is usually performed, so that alumina sol as a surface treating agent is added so that the amount in this range is attached to the titanium oxide.

Next, a method for preparing an aqueous dispersion slurry of titanium oxide will be described.

It is preferable that the water used has a high purity, and when it contains unnecessary ions and solids, it is desirable to remove them.

The titanium oxide slurry concentration is preferably 1 to 60% as a titanium oxide weight concentration when the total amount of water and titanium oxide is 100, and more preferably 5 to 30%.

If the slurry concentration exceeds 60 wt%, the slurry viscosity will increase and the contact frequency between titanium oxides will increase.
The surface treatment condition deteriorates. On the other hand, if it is less than 1 wt%, the processing efficiency is undesirably reduced.

When dispersing the titanium oxide in water, it is preferable to appropriately add and disperse a surfactant such as sodium hexametaphosphate.

As described above, the surface treatment of the titanium oxide is performed by mixing the prepared alumina sol and the titanium oxide slurry. In this mixing, mixing is performed while stirring the whole with an appropriate force. Is preferred.

In the present invention, since the alumina sol is prepared in advance, the mixing with the titanium oxide slurry can be continuously performed. Therefore, an impeller type stirrer or a static mixer may be used. However, too strong agitation is not preferable because it causes destruction of the surface coating on which titanium oxide is formed or instability of the alumina sol.

The slurry after mixing may be aged by continuing stirring as it is.

In addition, if alumina sol is kept in the sol state for a long time after preparation, effective film formation on the surface of titanium oxide cannot be performed efficiently. Depending on the storage condition of the alumina sol and the stirring intensity at the time of preparation, etc.
It is preferable to use it for mixing with the titanium oxide slurry within an hour.

The surface-treated slurry containing titanium oxide is dried after being filtered and, if necessary, washed with water. After drying, it is pulverized using a fluid energy pulverizer or the like to obtain a titanium oxide pigment.

〔Example〕

 Next, the present invention will be described in detail with reference to examples.

Example 1 Commercially available rutile-type titanium oxide (Showa Titanium Co., Ltd.)
20 g of “Super Titania G” was dispersed in 180 ml of pure water to prepare a titanium oxide slurry.

Next, separately from this, 1.8 ml of a 0.002 mol / dilute aqueous sulfuric acid solution was dropped into 200 ml of a 0.039 mol / aqueous sodium aluminate aqueous solution to prepare a sol containing fine particles of aluminum oxide hydrate.

Ten minutes after the preparation of the sol, the addition and mixing of the titanium oxide slurry were started.

This mixing is carried out in a beaker having an effective volume of 2, and at the time of mixing, stirring is performed at 170 rpm using a stirrer (impeller 100 mmφ), and stirring is continued to deposit aluminum oxide hydrate on the titanium oxide surface. Was performed. The time required for the surface treatment was 7 minutes.

The slurry after the surface treatment is applied to a membrane filter (0.2
μ), and the collected cake was dried at 170 ° C. for 12 hours. A commercially available automatic mortar (Knit-ANM-1000)
For 1 hour to obtain titanium oxide pigment powder.

Example 2 A titanium oxide slurry and an alumina sol were prepared under the same conditions as in Example 1.

However, in this case, 16 ml of 0.5 mol / sodium aluminate was used, and 0.5 mol / of dilute sulfuric acid aqueous solution was used.
7.2cc was used. The mixing of the slurry and the sol was performed using a magnetic stirrer in a 100 ml beaker.

The pH at the time of the surface treatment of titanium oxide was the same as in Example 1, and 8.
It was 15.

Thereafter, the slurry after the surface treatment was filtered using the same membrane filter as in Example 1, and the obtained cake was washed, dried and crushed to obtain a pigment powder.

Example 3 Commercially available anatase-type titanium oxide (Sakai Chemical Industry A-15
Except that 0) was used in place of the rutile type titanium oxide, treatment was performed under the same conditions as in Example 1 to obtain a titanium oxide pigment powder.

Example 4 The same 8.5 kg of anatase-type titanium oxide as in Example 3 was added to 77
Was dispersed in pure water to prepare a titanium oxide slurry.

Next, 272 g of commercially available sodium aluminate reagent (Kanto Chemical)
Was dissolved in water of 80 to adjust the pH to 8.20 by adding 0.15 mol / dilute sulfuric acid dropwise to prepare an alumina sol.

These slurries and sols were mixed in one pass using a commercially available static mixer (S-251-3B, Sakura Seisakusho). The processing time during that time was 10 minutes, during which time the surface treatment was performed.

The slurry after the surface treatment was filtered and washed with a 0.4 μm membrane filter, dried, and subjected to a pulverization step of a fluid energy mill to obtain a pigment powder.

Example 5 A 600 mol of Al (NO ₃ ) ₃ aqueous solution with a concentration of 0.033 mol /
13 ml of aqueous ammonia was added dropwise to adjust the pH to 8.5 to produce a sol containing fine particles of aluminum oxide hydrate.

The same titanium oxide slurry as in Example 1 was mixed with this sol.

Mixing was performed in a 500 cc beaker, and a magnetic stirrer (GP-H-1 manufactured by Shibata Chemical) was used as a stirrer.

The post-treatment of the slurry after the surface treatment is the same as in Example 1,
A pigment powder sample was obtained.

Example 6 An Al ₂ (SO ₄ ) ₃ aqueous solution having a concentration of 0.017 mol /
13 ml of aqueous ammonia was added dropwise to adjust the pH to 8.3 to produce a sol containing fine particles of aluminum oxide hydrate.

 Otherwise, a sample was prepared in the same manner as in Example 5.

Comparative Example 1 20 g of the same rutile-type titanium oxide as in Example 1 was added at 0.016 mol /
Was added to 500 cc of an aqueous sodium aluminate solution, and dispersed with a commercially available stirrer (blade diameter: 50 mmφ, rotation speed: 300 rpm).
Next, about 1.8 of a 0.002 mol / dilute aqueous sulfuric acid solution was added thereto over 1 hour and 20 minutes to adjust the final pH to 8.1.

Thereafter, the slurry was filtered, washed, dried and crushed in the same manner as in Example 1 to obtain a pigment powder.

Comparative Example 2 Except that the diluted sulfuric acid aqueous solution was dropped over 6 hours,
A treatment under the same conditions as in Comparative Example 1 was performed to obtain a pigment powder.

Next, with respect to the samples obtained in Examples 1 to 6 and Comparative Examples 1 and 2, the content of aluminum oxide hydrate was determined by analysis of an aluminum element using an induction plasma emission spectrometer (ICP). In addition, the presence or absence of gelled free aluminum oxide hydrate was examined by a transmission electron microscope (TEM). Table 1 shows the results.

In Table 1, the time required for the surface treatment refers to the sum of the time required for generating the sol and the time required for mixing the generated sol and the titanium oxide slurry in Examples 1 to 6, and 1 and 2 show the time required to complete the surface treatment by dropping the acidic solution onto the titanium oxide slurry.

[Effect of the Invention] According to the present invention, by causing the formation reaction of alumina sol as a surface treatment agent to be performed independently of the surface treatment reaction,
By preventing non-uniformity of the pH value during the surface treatment reaction step, it has become possible to quickly perform uniform, efficient and high-quality surface treatment.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-14819 (JP, A) JP-A-48-89937 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09C 1/00-3/12

Claims (1)

(57) [Claims] 1. A surface treatment of titanium oxide, wherein an aqueous dispersion slurry of titanium oxide and alumina sol are prepared in advance and mixed with each other when performing surface treatment with titanium oxide hydrate on titanium oxide. Method.